1. Field of the Invention
The present invention relates to a method for producing fullerenes. More particularly, the present invention relates to a method which enables one to mass-produce fullerenes from relatively inexpensive raw material.
2. Related Background Art
Since the discovery of fullerene C60 having a soccer ball-like polyhedral molecular structure comprising 60 carbon atoms by H. W. Kroto, R. E. Smallry and R. F. Curl, fullerene C70 with 70 carbon atoms, fullerene C76 with 76 carbon atoms, fullerene C78 with 78 carbon atoms, fullerene C82 with 82 carbon atoms, fullerene C84 with 84 carbon atoms, fullerene C86 with 86 carbon atoms, fullerene C88 with 88 carbon atoms, fullerene C90 with 90 carbon atoms, fullerene C94 with 94 carbon atoms, and fullerene C96 with 96 carbon atoms respectively having a soccer ball-like polyhedral molecular structure have been successively discovered. Besides, fullerenes containing metal elements therein have been also discovered. Along with the discovery of these fullerenes, various researches on their application use in functional devices and medicaments have been vigorously carrying out.
As the method of producing such fullerenes, there have been developed various methods such as a laser evaporation in heated flow gas method wherein fullerenes are extracted from a soot-like material produced by radiating a laser to a graphite in an argon or helium gas stream heated to high temperature of about 1200° C.; a resistive heating method wherein fullerenes are extracted from a soot-like material produced by energizing a graphite rod to heat the graphite rod in a helium gas atmosphere; an arc-discharge method wherein fullerenes are extracted from a carbon medium produced by generating arc-discharge between two graphite electrodes; a high frequency induction heating method wherein fullerenes are extracted from extracted from a soot-like material produced by heating and evaporating a graphite by flowing overcurrent therein by way of high frequency induction; and a burning method wherein fullerenes are extracted from a soot-like material produced by burning a mixed gas comprising benzene and oxygen which is diluted with argon gas.
Besides, Japanese Laid-open Patent Publication No. 5(1993)-186865 discloses a method for producing carbon clusters by subjecting a pair of electrodes comprising a carbon rod and a metal rod arranged in a vessel filled with inert gas to arc-discharging or resistive heating. Japanese Laid-open Patent Publication No. 6(1994)-56414 and Japanese Laid-open Patent Publication No.6(1994)-32606 disclose a method for producing fullerenes by isolating them from a solid material produced by supplying an aromatic compound in a heat plasma generated.
However, any of the above-mentioned methods for producing fullerenes has disadvantages such that the starting material and the apparatus used for practicing the method are costly, the yield is low, and it is difficult to quantitatively produce fullerenes at a reasonable production cost.